Soil Carbon Dioxide Fluxes From Switchgrass Land Under Nitrogen Fertility Management In South Dakota.

Switchgrass (Panicum virgatum L.), a perennial warm-season grass has been introduced as a potential biofuel crop in the United States. This crop has potential to mitigate greenhouse (GHG) fluxes; however, its production varies from region to region because of variable climate and soil type. This study was conducted near Bristol, SD USA on a Nutley-Sinai (silty clay, mixed, Chromic Hapluderts) soil to improve switchgrass biomass production with N fertility management based on local environments, and to evaluate the impacts on soil GHG fluxes. Specific objective was to assess the impact of N fertility management and landscape position on soil surface carbon dioxide (CO₂) fluxes. The experimental layout was a factorial design comprised of three N levels (low, 0 kg N ha^-1; medium, 56 kg N ha^-1; and high, 112 kg N ha^-1), and, two landscape (crest and toe) positions with four replications. Soil CO₂ fluxes were monitored bi-weekly using the static chamber technique from all 24 plots (2 chambers per plot) from 2010 through 2013. Data show that CO₂ fluxes were strongly influenced by landscape position and N levels. In general, high N rate increased CO₂ compared to that of control (0 kg N ha^-1) for 2010 and 2011, however, differences between medium and high N rates were not always large. Application of high N rate increases switchgrass biomass production, stimulates microbial activity and hence the fluxes. Further, soils at toe position had higher fluxes compared to that of crest. This is attributed to the fact that soils at toe position were well structured, aerated and wetter compared to those at crest and hence increased microbial decomposition of crop residue which increased fluxes. Results showed that switchgrass grown under crest position under different N rates produced lower CO₂ fluxes than at toe slope. However, a comprehensive life cycle analysis would be appropriate to evaluate environmental impacts associated with complete biofuel production systems under South Dakota conditions.